A quantum-dot cellular automata (QCA) is a technology whose excitons are confined in all three spatial dimensions. QCA have properties that are between those of bulk semiconductors and those of discrete molecules. QCA may be used in many applications, for example, in transistors, solar cells, LEDs, diode layers, as agents for medical imaging. QCA may further be used as qubits and as memory. QCA may operate at very high densities and very low power and may be used in many applications.